The present invention relates to a process for producing anaryloxyacetic acid, particularly to a process for producing an aryloxyacetic acid wherein an oxygen-containing gas is made act on an aryloxyethanol in an aqueous medium using a specific catalyst.
A process in which an oxygen-containing gas is made act on an aryloxyethanol by using a platinum-based catalyst in an alkali aqueous medium has been known as a process for producing an aryloxyacetic acid. For example, there have been known a process which uses platinum, or palladium and bismuth, or lead as a catalyst (JP-A-62-28940), a process which uses palladium and silver as a catalyst (JP-A-3-500653), and a process which uses palladium and antimony or tellurium as a catalyst (JP-A-3-38544).
However, these catalysts have a problem that catalyst components were eluted into the reaction mass after completion of the reactions. This problem has hindered recycling of the catalyst.
The present inventors have conducted extensive study to find a catalyst whose components are suppressed to be eluted into a reaction mass, and have found that catalysts comprising a combination of palladium and an indium compound and/or a copper compound are excellent in anti-elution property.
In known process for producing aryloxyacetic acid, the production is carried out in the presence of one or more equivalence ratio of alkali based on the raw material, aryloxyethanol. The present inventors have also conducted extensive study on a process which is carried out in the practical absence of alkali, and have found that among platinum-based catalysts, only catalysts containing platinum as a main component can exhibit an effect as an oxidation catalyst even in the practical absence of alkali.
The present inventors have made further investigation and have accomplished the present invention.
The present invention provides an industrially advantageous process for producing an aryloxyacetic acid represented by the formula (2): 
wherein m represents an integer of 1 or 2, n represents an integer from 0 to 4. Ar represents an aromatic hydrocarbon ring, each Rs independently represents an alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, a cycloalkoxy group, an aryloxy group, a halogen atom, an alkylcarbonyl group, an arylcarbonyl group, a carboxyl group or a nitro group,
comprising a step in which an oxygen-containing gas is made act on an aryloxyethanol represented by the formula (1):
xe2x80x83(R)n-Ar"Parenopenst"Oxe2x80x94CH2.CH2.OH)mxe2x80x83xe2x80x83(1)
wherein m, n, Ar and R, respectively, have the same meanings as defined above,
under conditions of using a catalyst comprising palladium and an indium compound and/or a copper compound in an aqueous medium and in the presence of 0.5 m or more equivalent of alkali per one mole of the aryloxyethanol represented by the formula (1); or
under conditions of using a platinum catalyst, in an aqueous medium and in the absence of alkali or in the presence of less than 0.5 m equivalent of alkali per one mole of the aryloxyethanol represented by the formula (1).
The present invention uses an aryloxyethanol represented by the above general formula (1) as a raw material In the formula, Ar represents an aromatic hydrocarbon ring. Examples of the aromatic hydrocarbon ring include benzene ring or naphthalene ring. When Ar is a benzene ring, the aryloxyethanol of formula (1) is represented by the general formula (1-1): 
wherein m, n, and R, respectively, have the same meanings as defined above.
In these formulae, each Rs independently represent an alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, a cycloalkoxy group, an aryloxy group, a halogen atom, an alkylcarbonyl group, an arylcarbonyl group, a carboxyl group or a nitro group.
Examples of the alkyl group as R include linear or branched hydrocarbon groups having from 1 to 12 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, t-butyl, pentyl, isopentyl, t-amyl, hexyl, isohexyl, heptyl, isoheptyl, t-octyl, isooctyl, nonyl, isononyl, decyl, ilsodecyl, undecyl, isoundecyl, dodecyl and isododecyl. Among them, linear or branched hydrocarbon groups having from 1 to 6 carbon atoms are preferred.
Examples of the cycloalkyl group include cyclic hydrocarbon groups having from 5 to 9 carbon atoms such as cyclopentyl and cyclohexyl Examples of the aryl group include phenyl and naphthyl. Examples of the alkoxy group include alkoxy groups having an alkyl moiety with from about 1 to about 12 carbon atoms, such as methoxy, ethoxy, propoxy, butoxy, isobutoxy, t-butoxy, pentoxy, isopentoxy, hexoxy and isohexoxy. Examples of the cycloalkoxy group include cyclopentoxy and cyclohexoxy Examples of the aryloxy group include phenoxy and naphthoxy.
The halogen atom includes fluorine, chlorine, bromine, iodine and the like, and preferred are chlorine and bromine. Preferred alkylcarbonyl groups are lower alkylcarbonyl groups having from 1 to 6 carbon atoms such as an acetyl group. Examples of the arylcarbonyl group include a benzoyl group.
Representative examples of the ayloxyethanol include 2-phenoxyethanol, 2-(2-methylphenoxy)ethanol, 2-(3-methylphenoxy)ethanol, 2-(4-methylphenoxy)ethanol, 2-(2-ethylphenoxy)ethanol, 2-(3-ethylphenoxy)ethanol, 2-(4-ethylphenoxy)ethanol, 2-(2-propylphenoxy)ethanol, 2-(3-propylphenoxy)ethanol, 2-(4-propylphenoxy)ethanol, 2-(2-isopropylphenoxy)ethanol, 2-(3-isopropylphenoxy)ethanol, 2-(4-isopropylphenoxy)ethanol, 2-(2-cyclopentylphenoxy)ethanol, 2-(3-cyclopentylphenoxy)ethanol, 2-(4-cyclopentylphenoxy)ethanol, 2-(2-cyclohexylphenoxy)ethanol, 2-(3-cyclohexylphenoxy)ethanol, 2-(4-cyclohexylphenoxy)ethanol, 2-(biphenyl-2-yloxy)ethanol, 2-(biphenyl-3-yloxy)ethanol, 2-(biphenyl-4-yloxy)ethanol, 2-(2-naphthalene-1-ylphenoxy)ethanol, 2-(3-naphthalene-1-ylphenoxy)ethanol, 2-(3-naphthalene-1-ylphenoxy)ethanol, 2-(2-naphthalene-2-ylphenoxy)ethanol, 2-(3-naphthalene-2-ylphenoxy)ethanol, 2-(4-naphthalene-2-ylphenoxy)ethanol, 2-(2-chlorophenoxy)ethanol, 2-(3-chlorophenoxy)ethanol, 2-(4-chlorophenoxy)ethanol, 2-(2-bromophenoxy)ethanol, 2-(3-bromophenoxy)ethanol, 2-(4-bromophenoxy)ethanol, 2-(2-acetylphenoxy)ethanol, 2-(3-acetylphenoxy)ethanol, 2-(4-acetylphenoxy)ethanol, 2-(2-benzoylphenoxy)ethanol, 2-(3-benzoylphenoxy)ethanol, 2-(4-benzoylphenoxy)ethanol, 2-(naphtalene-1-yloxy)ethanol, 2-(naphtalene-2-yloxy)ethanol, 1,2-bis(hydroxyethoxy)benzene, 1,3-bis(hydroxyethoxy)benzene, and 1,4-bis(hydroxyethoxy)benzene Among them, phenoxyethanol, 1,2-bis(hydroxyethoxy)benzene, 1,3-bis(hydroxyethoxy)benzene, and 1,4-bis(hydroxyethoxy)benzene and the like are preferable. Particularly preferred is 1,3-bis(hydroxyethoxy)benzene.
The present Invention provides a process in which an oxygen-containing gas is made act on the above-mentioned aryloxyethanol represented by the formula (1)
under conditions of using a catalyst comprising palladium and an indium compound and/or a copper compound (hereinafter, abbreviated by xe2x80x9cPd/In,Cu catalystxe2x80x9d) in an aqueous medium and in the presence of 0.5 m or more equivalent of alkali per one mole of the aryloxyethanol represented by the formula (1); or
under conditions of using a platinum catalyst (hereinafter, abbreviated by xe2x80x9cPt catalystsxe2x80x9d), in an aqueous medium, and in the absence of alkali or in the presence of less than 0.5 m equivalent of alkali per one mole of the aryloxyethanol represented by the formula (1).
In the present invention, when the oxygen-containing gas is made act in an aqueous medium and in the presence of 0.5 m or more equivalent of alkali per one mole of the aryloxyethanol represented by the formula (1), a catalyst comprising palladium as a first component and a copper compound and/or an indlum compound as a second component is used. An atomic ratio of the second component to palladium is generally from about 0.01 to about 20, preferably from about 0.1 to about 10.
The palladium useful in the catalyst of this invention can be in a variety of forms. Elemental palladium metal can be used. Other palladium compounds, such as the oxides, can also be used.
The copper and/or indium as the catalyst in this invention can be in a variety of forms and oxidation states. Examples of copper compounds which can be used include elemental copper metal, copper(I) salts, such as copper(I) oxide, and copper(II) salts. Examples of indium compounds which can be used are elemental indium, indium(I) salts, and indium(III) salts. By adding an indium compound and/or a copper compound to palladium, elution of palladium, indium and copper into the reaction solvent is suppressed.
In this case, a mixture of a first component and a second component or a compound thereof, composite oxides of these metals, materials obtained by coprecipitating these metals, and the like can be used as it is as a catalyst. Nevertheless, the catalyst are generally used with being supported on a carrier. Examples of the carrier include active carbon, silica gel, alumina, titania, zirconia, celite and diatom earth. Preferred is active carbon. Amount of the palladium supported on the carrier is from about 0.01 to about 30% by weight, preferably from about 0.1 to about 15% by weight relative to the weight of the carrier.
A method for making the carrier support the catalyst components thereon is not particularly limited. In general, a semi-arid supporting method, a precipitation supporting method, an equilibrium adsorption method, an ion adsorption method, an evaporation-to-dryness method, a spraying method and the like can be adopted. The catalyst components may be supported either at one time or sequentially. Further, activation may be carried out by kneading, baking or reduction, as needed. In the sequential supporting method, kneading, baking or reduction can be conducted either after supporting the first component and before supporting another component, or after supporting the first component and another component.
Amount of the catalyst to be used relative to the aryloxyethanol, the raw material, can be varied widely. Although it depends on a desired reaction rate, it is generally from 0.0001 to 1 atom, preferably from 0.005 to 0.5 atom, in terms of palladium, relative to 1 mol of the aryloxyethanol, for example, in the case of a slurry bed.
In the present invention, when the oxygen-containing gas is made act in an aqueous medium and In the absence of alkali or in the presence of less than 0.5 m equivalent of alkali per one mole of the aryloxyethanol represented by the formula (1), Pt catalyst is used. As the Pt catalyst, platinum, platinum oxide and platinum partially oxidized such as an Adams catalyst can be used. Generally, those supported on a carrier are used. Amount of the platinum supported on the carrier is usually from 0.1 to 25% by weight, preferably from 0.5 to 10% by weight. Examples of the carrier include activated carbon such as peat, charcoal, coconut shell coal and animal charcoal, activated clay, titania, zirconia, alumina and zeolite. Among them, those supported on an activated carbon, particularly peat, are preferably used. The Pt catalyst can contain metals other than platinum as a promoter. Example of the metals other than platinum include bismuth, antimony, germanium, tin, lead, gallium, indlum, thalliumandtellurium. Among them, bismuth, tellurium, lead and the like are preferred, and bismuth is particularly preferred. An amount of the metal other than platinum on the carrier is usually from 0.1 to 30% by weight, preferably from 0.5 to 20% by weight based on the total amount of catalyst.
When the catalyst contains platinum and bismuth, it is preferable that the catalyst also contain one or more metals such as chromium, molybdenum, tungsten, vanadium, niobium, tantalum, germanium, tin and lead. Amount of the metal other than platinum and bismuth on the carrier is usually from 0.1 to 30% by weight, preferably from 0.5 to 20% by weight based on the total amount of catalyst.
Amount, relative to the aryloxyethanol, of the Pt catalyst to be used can be varied widely. Although it depends on a desired reaction rate, it is generally from 0.001 to 0.1 atom, preferably from 0.005 to 0.05 atom, in terms of platinum, relative to 1 mol of the aryloxyethanol, for example, in the case of a slurry bed.
In the present invention, the oxygen-containing gas is made act on an alkyloxyethanol of formula (1) in an aqueous medium. Examples of the aqueous medium include water and mixed solvents consisting of water and a lower carboxylic acid, such as aqueous acetic acid and aqueous propionic acid. Among them, water is preferably used. The aqueous medium can also contain a surfactant inert to the reaction, an organic solvent, and the like.
Amount, by weight, of the aqueous medium to be used is generally from about 1 to about 30 times, preferably from about 5 to about 15 times, based on the amount of the aryloxyethanol.
In the present invention, when Pd/In,Cu catalyst is used, amount of the alkaline substance to be used is usually from about 0.5 m to about 30 m equivalents, preferably from about 0.8 m to about 10 m equivalents per one mole of the aryloxyethanol represented by the formula (1), wherein m has the same meaning as defined in the formula (1).
Examples of the alkaline substance include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, alkali earth metal hydroxides such as calcium hydroxide, magnesium hydroxide, alkali metal carbonates such as sodium carbonate, potassium carbonate, alkali metal hydrogen carbonates such as sodium hydrogen carbonate, potassium hydrogen carbonate, organic bases such as aniline, diethylamlne, triethylamine, pyridine, and ammonia. Among them, sodium hydroxide is preferably used.
In the present invention, when Pt catalyst is used, amount of the alkaline substance to be used is less than 0.5 m equivalents, preferably less than 0.2 m equivalent, per one mole of the aryloxyethanol represented by the formula (1), wherein m has the same meaning as defined in the formula (1).
If the aryloxyethanol is produced by using a small amount of alkali in its producing process, it may be applied for the reaction of the present invention in which Pt catalyst is used after neutralizing the alkali and also may be used without neutralizing the alkali.
In the reaction of the present invention, the use of alkaline substance is preferable for increasing reaction rate. However, even in the absence of alkali, the reaction can be carried out by using the Pt catalyst.
When using Pt catalyst, the alkali can exist from the beginning of the reaction, and it also can be added in the middle of the reaction. When the alkali is added in the middle of the reaction, the amount of alkali which exists at the beginning is preferably less than 0.1 m equivalents, more preferably 0.05 m equivalents, and the total amount of alkali is less than 0.5 m equivalents per one mole of the aryloxyethanol.
The alkaline substance can be added successively or intermittently.
In both cases of using Pd/In,Cu catalyst and using Pt catalyst, the oxygen-containing gas may be oxygen gas, mixed gas of oxygen and gas inert to the reaction such as nitrogen, argon. To regulate the partial pressure of oxygen, mixed gas of oxygen and nitrogen can be used. Air is preferred because of its low price, and mixed gas of air and nitrogen can be used to regulate the partial pressure of oxygen.
The reaction pressure is generally from about 0.05 MPa to about 10 MPa, preferably from about 0.1 MPa to about 3 MPa.
Although the reaction temperature is not particularly limited, it is usually from about 10xc2x0 C. to about a boiling temperature under reaction conditions, preferably from about 50xc2x0 C. to about the boiling temperature under reaction conditions.
The reaction in the present invention may be carried out in either a batch system or a continuous system. A type of a reactor may be any one of a slurry bed, a fixed bed, a fluidized bed, and a trickle-bed.
Progress of the reaction can be traced with a high performance liquid chromatography, gas chromatography, etc. It can also be traced by the measurement of oxygen absorbed.
Thus the target compound, the aryloxyacetic acid represented by the formula (2), can be obtained. When the reaction is carried out in the alkaline aqueous medium, the target compound can be isolated, for example, by separating the catalyst from the reaction mass by filtration or the like, neutralizing or acidifying the filtrate with acid, if necessary, followed by concentration, and then collecting crystals by filtration. Alternatively, the target compound can be isolated by neutralizing or acidifying the filtrate with acid, then extracting the filtrate with a hydrophobic organic solvent, followed by evaporating the solvent from the extract. In the case where the reaction is carried out in the practical absence of an alkali, the target compound can be isolated, for example, by separating the catalyst from the reaction mass by filtration and then concentrating the filtrate. It can also be isolated by extracting the reaction mass with a hydrophobic organic solvent and then evaporating the solvent. The isolated target compound can be further purified through purifying operations such as distillation, recrystallization, extraction and chromatography, as needed.
According to the present invention, when a specific catalyst in which palladium and an indium compound and/or a copper compound are combined is used, elution of the catalyst components into a reaction mass can be suppressed.
Further, the desired aryloxyacetic acid represented by the formula (2) can be produced even in the practical absence of alkali by using a specific catalyst, Pt catalyst. Consequently, amount of alkali required for producing the aryloxyacetic acid can be reduced. Moreover, in the process which is carried out in the presence of alkali, since the aryloxyacetic acid of formula (2) is obtained in the form of an alkali salt, an equivalent amount of acid relative to the alakali is required for neutralization. In contrast, by carrying out the production of the aryloxyacetic acid of formula (2) in the practical absence of alkali, a drastic reduction of the use of acid and an omission of the neutralization step can be achieved.